The present invention relates to oscillators and, more particularly, circuitry and method for providing isolation between the oscillator output and the feedback path to the input of the gain producing device of the oscillator to improve the operating characteristics thereof.
In general, most, if not all, oscillators include a two port gain producing device having an input and an output which produces an output signal at the output of the oscillator and feedback between the output and the input of the device of proper phase and gain to induce and sustain oscillation. There are a myriad of structures and methods for providing a feedback path to couple a portion of the output signal from the gain producing device back to its input. However, in all known oscillators the feedback path is not inherently isolated from the output of the oscillator wherein the phase of the feedback signal becomes a function of the characteristics of the load coupled to the output of the oscillator. This lack of isolation is critical in that large changes in the frequency and output power of the oscillator can be caused by a change in the impedance of the oscillator load. In the extreme, oscillation may not be sustained and the device could be destroyed due to extreme load mismatching.
Hence, a need exists for an improved oscillator in which isolation is provided between the output of the oscillator and the feedback path to the input of the gain producing device thereof for improving the frequency and power pulling characteristics of the oscillator.